Continuous coking



Oct. 7, 1958 A. H. SCHUTTE CONTINUOUS coKING Filed oct. 28,1954

' ATT v United States Patent O CONTINUOUS CoKING August Henry Schutte,Hastings-on-Hudson, N. Y., as-

signor to The Lummus Company, New York, N. Y., a corporation of DelawareApplication October 28, 1954, Serial No. 465,342

4 Claims. (Cl. 208-126) This invention relates to a continuous contactcoking process for the conversion of heavy liquid hydrocarbons in liquidphase to gas or vapors and dry solids. It is a modification of theinvention disclosed in the present pending application, Serial No.252,306, led October 20, 1951, now abandoned, and is an improvement onthe disclosure in U. S. Patent 2,561,334 of which I am a coinventor.

It has been established that the circulation of solid granularparticles, particularly coke, through a reaction zone, a reheating zone,and a return conduit serves as an entirely satisfactory medium for vtransferring heat to heavy hydrocarbon residuum whereby completeconversion to -gas and vapors and' solids is possible. As described inthe patent `above referred to, it is the practice to pass the granularmaterial downward as a compact gravity moving column through a closedreactionzone during which the liquid applied is converted into thedesired end products. It has been 'found desirable to maintain thereaction conditions for at least tive minutes by restricting theresidence time Of contact particles to complete reaction in order thatthe particles may go through the period of tackiness during movement andmay thereafter be removed in a completely dry condition.

My past experience indicates that the heat exchange particles can beused for supplying the necessary heat of conversion to an oil chargethat is relatively cooler than the particles themselves. If, however,the oil is `at a temperature below reaction temperature it is necessaryto reheat the particles to a relatively high degree and this has causedsome complications because of the high temperature involved.Furthermore, it is relatively difficult to obtain absolute uniformity ofcoke particle temperature.

More recently, I have observed thatthe heat balancev in the coke reactordoes not require the large amount of heat heretofore thought necessaryand it is now apparent that lower operating temperatures are entirelypractical. This reduction in the temperature level reduces the gas andgasoline production with a corresponding increase in the yield of gasoil and makes for a more eiicient unit.

In some cases it will be advantageous and economical to maintain theheat balance throughout the reactor by a combination of heat additionwith the oil charge plus the introduction of superheated steam into astripping section of the reactor at a temperature well above the averagereaction temperature. The heat losses inherent in the exterior solidscirculating system may also be compensated by utilizing highlysuperheated steam in the parl ticle recirculation and elevating portionof the system.

Vice

higher than the average reactor temperature and the heat required tocomplete the drying-out of the newly deposited coke ilm on the particlesin the lower or stripping section of the reactor was provided by heat owfrom'the interior of'the coke particle to its exterior surface.

In my present invention the newly formed coke film on the coke particlesin the drying or stripping zone of the reactor is provided withheat fordrying by direct contact between the outer surface of the particles andcounterflowing superheated steam. It will be observed that my presentsystem requires the addition of only enough heat to the particles toraise the temperature of the outside surface of these particles. Thisquantity of heat, which is supplied by the superheated steam at atemperature above that of the average reactor temperature is thereforemuch less than in the case of the previously disclosed mechanismswherein the final drying-out of the coke iilm is4 accomplished 4by heatow from the particle interior.

The primary advantage, however, of the lower heat requirement is that Inow nd it possible to increase the temperature of the feed stock, thussupplying the heat of vapors in a tubular heater and thereby eliminatingthe separate reheating of the coke. Such operation thus eliminates oneof the major elements of apparatus and materially reduces the -operatingcosts and controls.

More particularly, my present invention is based on the discovery thatunder suitable conditions the charge stock may be heated to a higherdegree than required for the reaction and suicient to be used to restorethe nominal heat losses of particle heat exchange material by directapplication of the heated charge stock during recirculation of theparticles. The granular heat exchange material thus serves primarily asa surface for the deposit of coke and not primarily as a reservoir forreaction heat with the result that the design of the reactor may bebased upon particle surface requirements rather than the solids-to-oilratio dictated by heat balance requirements.

Further objects and advantages of my invention will appear from thefollowing disclosure of a preferred form of embodiment thereof taken inconnection with the attached drawing in which the iigure is a schematicelevation with parts in section, of the major elements of a continuouscontact coking system in accordance with my invention.

The preferred form of apparatus to carry out my invention generallyincludes a sealed reaction zone which may conveniently be a cylindricalvessel 10 through which coke particles are circulated in the system ashereinafter described. These particles, which may be as described in mypatent, 2,600,078, are introduced into the reaction Zone 10 through theinlet conduit 12. The liquid charge is preferably introduced to thesecoke particles while in the lift conduit 12 by the charge inlet line 14.

In the reaction zone 10 which is maintained at aboutv 825 to 875 F., arapid conversion of the charge material takes place with an outlet ofthe gaseous end products through the line 16. Below this gas and vaporoutlet 16 is preferably mounted a stripper section 18 suitably fed bysuperheated steam at 20 to assure complete removal of all vapors and thecomplete drying of deposited carbon residue on the particles.

The coke particles continue to move by gravity and discharge through theoutlet 22 into a lock tank 24 and theny into a lift tank 26 from whichthey are elevated by mass lift flow, which may be as described in myPatent 2,684,929 through the lift conduit 12 to the top of the reactor.By the use of the tandem vessels 24 and 26 and suitable valves 27 and 28as well as control steam through line 2.9 with appropriate controls notshown, it is possible to maintain a complete uniformity of coke particleow and maintain a pressure within the reactor 10 of from one atmosphereto 100 p. s. i. g. It is, of course, understood that the lock tank 24 isprovided with a suitable vent as at 30 and it may also be provided witha coke charge inlet shown at 32. If it is desired to remove cokeparticles, this may be done at 34 also under the control of a suit ableseparate valve.

In accordance with my preferred form of embodiment the oil charge at 36is preferably pumped through a fluid heater 38 wherein it is heated to atemperature above the desired reaction temperature. Assuming for examplea `desired reaction temperatureof about 850 F., it is found desirable toheat the oil to about 940 F.

Considering that some stocks would tend to coke under such temperaturesit is contemplated that the heater 38 will be designed for a shortresidence time under a pressure of 10-100 p. s. i. g.

The application of the hot oil to the coke particles will restore theparticle heat losses in the reactor and in the transfer from thereaction zone back to the upper part of the lift line and will bringsuch particles back to the desired reaction temperature. It is myexperience that the particles, when not reheated, drop from 5-.10 F.from the time of the reaction until they can be circulated to the upperpart of the reaction zone.

Due to the ratio of oil to coke, which is about 1 part to by weight anddue to the differences in heat characteristics it is necessary to heatthe oil to such a superior temperature of from 50 to 100 F. above thereaction temperature to establish the desired uniform temperatureconditions in the reactor.

The condition of particle ow in the lift line must be such thatpremature coking of the oil charge will not occur and so that there willbe nearly uniform distribution of the oil over the surfaces ofrecirculating particles.

I also find it desirable to supplement the heat in the reactor by theuse of steam heated to about l000 F. and introduced through the line 20to the desired extent. The relatively small amount of heat available inthis steam, above reaction temperature, is nevertheless very effectivein that Vit heats the outer surface of the particles rapidly and driesout the newly deposited coke lm. It will be understood that superheatedsteam will be removed with the vapors through the line 16 and will passto a fractionator not shown.

It has been found that with operation under the above temperatureconditions of about 940 F. for the oil charge and about 850 F. reactiontemperature, it is possibleA to charge 1000 bbls. per day of a heavyresidue to the coke particles which circulate at a rate of between 50and 100 tons per hour.

The reactor pressure is set so as to obtain an average temperature highenough to permit substantial drying out of the coke particles beforeentering the lower section where they are stripped with high temperaturesuperheated steam.

The particle size for uniform operation should not be of too broad arange and while I prefer to limit the range from about VlS" to M" majordimension, I have operated with as low as 50 mesh and as large as 11/2".I also nd that the particles grow or increase in size by about .001 inchcoating per pass. 4

A typical example of the application of a heavy hydrocarbon to acontinuously moving petroleum coke particle mass is as follows:

Charge-18 A. P. I. Illinois reduced crude:

Ramsbottom carbon-8.6 weight percent 20% distillation temp-755 F.

50% distillation temp-985 F.

Particle material-dense petroleum (equilibrium) coke:

Size-average, lAG to l maximum.- Apparent density-0.89 g./cc., orapprox. 60 lbs.

per cu. ft. Particle density- 1.39 g./cc.; particle porosity approx..03.

Procedura-1000 bbls. per day of oil charge is introduced at 940 F. tothe particle recirculation line; through which 70 tons per hour of drycoke is passed. Particle temperature in the recirculation line prior toentry of the charge is 845 F. The heat in the reactor is supple mentedby the use of-600 lbs. per hour of superheated steam at a temperature of1000 F. The temperature of the reactor outlet is 850 F.

The particles in the reactor column move downwardly from their point ofentry for a distance of approximately 15 feet before reaching the bottomof the conversion zone and the average particle residence time isapproximately 30 minutes to allow a full and complete conversion. Thecoke is removed as a free flowing homogeneous stream.

The foregoing example is illustrative of the operational features of myprocess but is not to be considered limiting thereof and I desire tocomprehend within my invention such modifications as are included withinthe scope of the following claims.

I claim:

1. The method of continuously converting a charge of heavy liquidhydrocarbons into coke and lower boiling hydrocarbon vapors in thepresence of discrete particles forming a contact mass, which comprisesmoving the particle mass downwardly through a reaction space as anunagitated gravity packed column, applying said charge to the particlesat a temperature above the conversion temperature and above thetemperature of the mass so as to heat the particles of such mass andmaintain a reaction temperature sulhcient for complete conversion of thecharge, retaining the particles of said downwardly moving column in thereaction space after application of said charge for at least fiveminutes and suciently long to complete the conversion of said charge toa dry, non-agglomerating coke deposit on the particles and a vaporousproduct including lower boiling hydrocarbon vapors, injectingsuperheated steam into said reaction space adjacent the bottom thereoffor completely drying said coke bearing particles, withdrawing the lowerboiling hydrocarbon vapors and steam from the reaction space, separatelywithdrawing the particles bearing dry coke from said reaction space, andrecirculating at least a portion of said coke bearing particles to thereaction space to provide the downwardly moving particle mass.

2. The method of continuously converting a charge of heavy hydrocarbonsinto dry carbon residue and lower boiling hydrocarbon vapors as claimedin claim 1 wherein the discrete particles are coke of at least 50 meshand predominantly in the range of 1/16 to 3A inch in diameter.

3. The method of continuously converting a charge of heavy hydrocarbonsinto a dry carbon residue and lower boiling hydrocarbon vapors asclaimed in claim 1 wherein the charge is heated to a temperature of from50 to 100 F. above the reaction temperature to replace heat lost by thedeposit bearing particles during recirculation and in which the pressurein the reaction section is `from one atmosphere to p. s. i. g. and thecharge is applied to the recirculating particles.

4. The method of continuously converting a charge of heavy liquidhydrocarbons into coke and lower boiling hydrocarbon vapors in thepresence of discrete contact particles, which comprises maintaining adescending unagitated gravity packed bed of particles within a reactionzone, continuously supplying particles to the upper portion of said bed,heating said heavy charge to a temperature above the conversiontemperature and above the temperature of the particles supplied to saidbed, ap plying said hot charge to the particles supplied to said bedwhereby said particles are heated and said bed is maintained at atemperature sucient for complete conversion of said charge, retainingthe particles of said bed in said reaction zone after application ofsaid charge for at least five minutes and sufficiently long to completethe conversion of said charge to a dry, nonagglomerating coke deposit onsaid particles and a vaporous product including lower boilinghydrocarbon vapors, injecting superheated steam into said reaction zoneadjacent the bottom thereof for completely drying said coke bearingparticles, withdrawing said lower boiling hydrocarbon vapors and steamfrom said reaction zone, separately withdrawing said coke bearingparticles from said reaction zone, and recirculating at least a portionof said coke bearing particles to said reaction zone to provide theparticles supplied to the upper por- 5 tion of said bed.

References Cited in the le of this patent UNlTED STATES PATENTS 1()2,477,502 Utterback et al. July 16, 1949 2,482,138 Schutte Sept. 20,1949 2,482,139 Schutte Sept. 20, 1949 2,719,114 Leiter Sept. 27, 1955

1. THE METHOD OF CONTINUOUSLY CONVERTING A CHARGE OF HEAVY LIQUIDHYDROCARBONS INTO COKE AND LOWER BOILING HYDROCARBON VAPORS IN THEPRESENCE OF DISCRETE PARTICLES FORMING A CONTACT MASS, WHICH COMPRISESMOVING THE PARTICLE MASS DOWNWARDLY THROUGH A REACTION SPACE AS ANUNAGITATED GRAVITY PACKED COLUMN, APPLYING SAID CHARGE TO THE PARTICLESAT A TEMPERATURE ABOVE THE CONVERSION TEMPERATURE AND ABOVE THETEMPERATURE OF THE MASS SO AS TO HEAT THE PARTICLES OF SUCH MASS ANDMAINTAIN A REACTION TEMPERATURES SUFFICIENT FOR COMPLETE CONVERSION OFTHE CHARGE, RETAINING THE PARTICLES OF SAID DOWNWARDLY MOVING COLUMN INTHE REACTION SPACE AFTER APPLICATION OF SAID CHARGE FOR AT LEAST FIVEMINUTES AND SUFFICIENTLY LONG TO COMPLETE THE CONVERSION OF SAID CHARGETO A DRY, NON-AGGLOMERATING COKE DEPOSIT ON THE PARTICLES AND A VAPOROUSPRODUCT INCLUDING LOWER BOILING HYDROCARBON VAPORS, INJECTINGSUPERHEATED STEAM INTO SAID REACTION SPACED ADJACENT THE BOTTOM THEREOFFOR COMPLETELY DRYING SAID COKE BEARING PARTICLES, WITHDRAWING THE LOWERBOILING HYDROCARBON VAPORS AND STEAM FROM THE REACTION SPACE, SEPARATELYWITHDRAWING THE PARTICLES BEARING DRY COKE FROM SAID REACTION SPACE, ANDRECIRCULATING AT LEAST A PORTION OF SAID COKE BEARING PARTICLES TO THEREACTION SPACE TO PROVIDE THE DOWNWARDLY MOVING PARTICLE MASS.